The present invention is generally directed to a television system which is capable of concurrently distributing multiple video presentations having different video information content over a single television channel for receipt by different respective viewers. For example, a television system in accordance with the present invention can distribute one or more broadcast video presentations as well as interactive service presentations from a central presentation system, to respective viewers with associated television sets and terminals, by means of a single television channel.
An interactive still frame television distribution system is disclosed, for example, in U.S. Pat. No. 4,734,764. Such a system is particularly suited for interactive video services such as home shopping, financial transactions, education and the like. Generally speaking, in this type of system a viewer sends an indication to a central location describing a video presentation which he desires to receive, e.g. houses being offered for sale by a real estate service. Video frames which show the available houses are individually retrieved from a suitable video storage medium, and each frame is labelled with an identification code which enables it to be retrieved by the viewer who desires to see it. Other viewers can independently request other presentations available on the system. All of the frames selected by the various viewers are multiplexed onto a transmission medium, such as the trunk cable of a cable television system, and transmitted at the standard television frame rate, e.g. 30 frames per second under the NTSC standard, over a channel associated with the video presentation service. Frame stores are positioned at various locations along the length of the transmission medium, and each is provided with a match code, for example an address. When a video frame is labelled with the match code of a particular frame store, that frame store identifies the frame, stores it in a memory, and then continually retransmits the stored frame at the standard television frame rate to the viewer""television receiver. The continually transmitted frame appears as a still frame on the viewer""s television receiver. When the next frame in the presentation is required, this frame is retrieved, labelled with the appropriate code, and transmitted to the frame store for display in the same manner. This process is repeated for all the frames in the still-frame presentation.
A sequence of frames may be sent for each still-frame presentation. If still frames are delivered at sufficient rate, the presentation takes on the appearance of reduced motion rather than distinct still frames. For example, if frames are sent at a rate of 6 per second, 5 concurrent user presentations are possible over a single television channel (having 30 frame per second capacity) with reduced motion. Additional processing within the frame store unit can interpolate several images to display additional images, with the object of producing the appearance of smoother motion.
With increasing acceptance of the value of interactive television system services, there is a clear benefit to the industry to provide an efficient transmission medium for these services. The high cost of dedicating a television channel solely to an interactive service is viable only for the largest of such services. Furthermore, it is highly desirable to include interactive capabilities with many of the broadcast services, such as distance learning, being transmitted via satellite, to provide a means for measuring the effectiveness of these services. Combining the transmission of interactive services with these services on one channel would save the cost of an additional channel while providing the benefits of interactive capabilities.
Accordingly, it is an object of the present invention to provide a television system which expands the program capacity of each channel of the television system by distributing at least two distinct presentations concurrently on a single channel. It is a further object of the present invention to address the above-mentioned needs by providing a television system which is capable of distributing multiple viewer requested (interactive) and/or broadcast video presentations, to different respective viewers by means of a single television channel, including the combination of full motion, reduced motion and still-frame video presentations. It is a further object of the present invention to provide a combination of presentations that be dynamically variable so that the system can respond to changing presentation requests over time.
The present invention provides a television system which increases the capacity of television channels by exploiting the fact that certain presentations do not require the full image capacity of a dedicated television channel and therefore the excess capacity can be used to distribute images of additional presentations over that channel. A television signal having multiple video presentations is transmitted over a single television channel. In an exemplary embodiment of the invention, one video presentation could comprise a motion video program and other presentations could pertain to a still-frame interactive video service. The television signal is produced by a multiplexer which combines the still-frame interactive video images and motion video images into a standard (such as NTSC) sequence of images for transmission.
In one embodiment of the invention, each of the interactive video images has an identification associated therewith so that these images can be distinguished from the full motion video images, which have a distinct associated identification. A user terminal which receives the transmitted television signal can be selectably operable to display different presentations. A selection corresponds to one of the video presentations transmitted in the television signal, and causes a television receiver connected thereto to display only the corresponding video presentation. In the specific example described above, the terminal can display either the motion presentation or a still-frame interactive presentation. To display a selected presentation, the terminal identifies the video images of the television signal corresponding to the selected presentation, stores the selected images, and displays them on an associated television set. Interactive instructions between a user at the terminal end and the presentation system are carried out via the use of a communication link such as a telephone line.
Other applications of the invention are also possible. The television signal could combine two or more motion video presentations whose content is such that each presentation can be displayed at less than the standard television rate without significant quality loss to the viewer. For example, the video presentations could be a movie and a set of educational programs, where the educational programs are scheduled to be broadcast sequentially, concurrent with the movie broadcast. Also, if two full motion video presentations are transmitted in the television signal, each one could be transmitted at a rate of 30 distinct fields per second for a total of 60 fields per second as specified by the NTSC standard. Additional applications of the invention are to provide two motion channels at 24 fields per second each, leaving 12 fields per second as excess capacity for interactive service presentations, or to provide 3 motion presentations at rates of 30, 15 and 15 fields per second respectively. The invention is dynamically variable due to the per image identification so that these applications needs can be established on a real-time basis.
The invention extends to a digital as well as analog (such as NTSC) transmission format where images are labelled with an identifier. Under a digital television format, additional digital processing such as image compression permits even greater dynamic variation in the tradeoffs between image transmission rate, image resolution and degree of compression.